Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

In the absence of annotations, the description carries the burden of transparency. It discloses the exact number of countries (218) and the metadata fields (region, income level, capital), setting expectations for the response. The operation is inherently read-only (a list), so no side effects are implied. However, it doesn't mention auth requirements or response format, but for a simple list this is sufficient.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single sentence that is front-loaded with the action ('List') and the resource ('all 218 countries'). It includes metadata details without any fluff. Every word earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the simplicity of the tool (one optional parameter, no output schema), the description is fairly complete. It clearly states the output scope and the included metadata fields, and the behavior with and without the region filter is implied. It doesn't describe the exact response structure, but for a list operation this is not a critical gap.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema already documents the single optional parameter 'region' with 'Optional: filter by region' at 100% coverage. The description does not add further meaning to this parameter beyond what the schema provides, so a baseline score of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's purpose: 'List all 218 countries with metadata (region, income level, capital).' The verb 'list' is specific, the resource is 'countries', and the scope ('all 218') is explicit. This distinguishes it from sibling tools like compare_countries or get_country_overview, which serve different purposes.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies usage for obtaining a full list of countries, but it does not explicitly state when to use this tool versus alternatives, nor does it provide any exclusion criteria. For example, it doesn't say 'use get_country_overview for detailed single-country info.' This is implied but not explicitly guided.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.